my $input = '(((';

grammar Test {
    token TOP {
        ^<down>*$
    }

    token down {
        ^\($
    }
}

class TestActions {
    method TOP ($/) {
        $/.make($<down>.map({.made}));
    }
    method down ($/) {
        $/.make(1);
    }
}

my $actions = TestActions.new;
my $res = Test.parse($input, :$actions);
say $res.made;